1. Technical Field
The present invention relates to electric circuits and, more particularly, to a method and apparatus for detecting and locating circuit defects.
2. Description of Related Art
In a test process of the manufacturing processes of a large scale integrated (LSI) circuit, it is difficult to detect a short circuit point. Specifically, in a case of completion of an LSI circuit such as an application specific integrated circuit (ASIC) ordered by a user for delivery within a short period of time, a short circuit problem sometimes occurs. A short circuit is typically formed between a plurality of power supply wiring patterns because there are crosses between power supply wiring patterns and because bugs of wiring design data, error in setting the coordinates of wiring patterns, or overlapping wiring patterns are occasionally introduced in the computer aided design (CAD) process. Such a type of short circuit between the power supply wiring patterns is the cause of incomplete operation of logic circuits as a main functional circuit of the ASIC.
In highly integrated circuits, it is very difficult to detect a point where the short circuit is formed. Conventionally, there is a method of visually checking the wiring mask pattern as a method of detecting a short circuit point between wiring patterns. However, it is impossible to completely check the wiring mask pattern for a large scaled integrated (VLSI) circuit layout.
A more sophisticated method of detecting circuit defects uses a combination of heat and voltage injection. These methods allow detection of circuit defects that are not observable visually. These methods involve heating the entire circuit assembly and then cooling sections of the assembly with compressed gas or liquid to locate probable defective components. However, subjecting electronic components to this rapid temperature change introduces structural damage to the components and, ultimately, causes degradation or failure of the component under normal operating conditions. Furthermore, the machines needed to perform this method are very costly and complicated to use. Therefore, a method and apparatus that allows detection and location of defects within a circuit to ensure the highest confidence in the integrity of the component assembly being repaired which does not damage the circuitry and that maintains lower production costs is desirable.
The present invention provides a method and apparatus for detecting and locating a circuit defect. In a preferred embodiment, the apparatus includes a resistance measuring device for measuring the resistance of the circuit, a heat source, and a recorder. The heat source is placed near the surface of the circuit but is not placed in physical contact with the surface. The heat source is moved about to a plurality of points in a plane parallel to and above the surface of the circuit while the resistance of the circuit is measured when the heat source is at each of the points. The recorder is functionally connected to the resistance measuring device and to the heat source, and determines and records the horizontal location of the heat source and records the resistance of the circuit at each of these locations.